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<h1>Advanced Topics</h1>
<p>This topic is about advanced features of db4o. </p>
<p>If you want to have multiple unit of work or multiple transaction in embedded mode you can take a look at session containers. <a href="advanced_topics/session_containers.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Session Containers"</a></p>
<p>db4o support unique constrains on fields. <a href="advanced_topics/unique_constraints.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Unique Constraints"</a></p>
<p>You can also do backups of your database at runtime. <a href="advanced_topics/backup.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Backup"</a></p>
<p>Implementing the interfaces for transparent activation/persistence is tedious. The enhancement tools can do that job for you. And can also optimize native queries at build time. <a href="advanced_topics/enhancement_tools.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Enhancement Tools"</a> <![CDATA[ ]]></p>
<p>The database file can fragment over time. In order to reclaim defragmentet space in the database you need to run the defragmentation. <a href="advanced_topics/defragment.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Defragment"</a></p>
<p><span class="MCPopup"><a href="javascript:void(0);" class="MCPopupSpot" onclick="FMCPopup( event, this ); return false;" MadCap:src="advanced_topics/callbacks.htm">Callback<img style="border: none;margin-left: 5px;" src="SkinSupport/ExpandingClosed.gif" MadCap:altsrc="SkinSupport/ExpandingOpen.gif" class="MCExpandingIcon" onload="if ( typeof( FMCPreloadImage ) == 'function' ) { FMCPreloadImage( 'SkinSupport/ExpandingOpen.gif' ); }" /></a></span> allow you to perform additional logic for different database operations. <a href="advanced_topics/callbacks.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Callbacks"</a></p>
<p>As some point in time you will change your data model. Then you probably need to also refactor you're stored data in the database. <a href="advanced_topics/refactoring_and_schema_evolution.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Refactoring and Schema Evolution"</a></p>
<p>You can access the internal ids or generate UUIDs for objects. <a href="advanced_topics/ids_and_uuids.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "IDs and UUIDs"</a></p>
<p>It's also possible to access the meta information of all stored types in the database. <a href="advanced_topics/db4o_meta-information.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "db4o Meta-Information"</a>. And you can access system information about the database.</p>
<p>db4o tried hard to make persisting objects as easy as possible. However storing a object efficient and correctly is quite tricky. Read about db4o's type handling for more information. <a href="advanced_topics/type_handling.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Type Handling"</a> Furthermore db4o uses an abstraction layer to encapsulate <span class="PrimaryPlattform">.NET</span>-reflection. This allows you do change how reflection behaves on your objects. <a href="advanced_topics/db4o_reflection_api.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "db4o Reflection API"</a></p>
<p>Unfortunately failure happen. db4o communicates failures with exceptions. <a href="advanced_topics/exceptions.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Exception-Handling"</a></p>
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